Forges 101

[Frosty]

Burner position is different in a melter too. While it can be done no tool designed to do everything does anything well.

Frosty The Lucky.

[Mikey98118]

4 hours ago, Frosty said:

no tool designed to do everything does nothing well.

I agree in principle. But, pushing the envelope is just sooo Mikey

[Mikey98118]

Another limitation in forge/furnace design is burner positioning. While the flame can be pointed in several ways in a forge, the flame in a casting furnace is aimed to impinge on the furnace wall as far forward as possible, without directly impinging on the crucible (since this promotes early crucible failure). If the flames in a forge were aimed this way, they would not burn for a long enough distance before impinging on work pieces, if the burner(s) should be pointed downward, toward the floor area. In these days of greatly improved refractories, it is better to aim them upward and slightly inward, to ensure the longest possible exhaust path in most forges; the exception being forges designed to create a hot spot, but there always are some limitations

[Frosty]

Pushing is the only reason for envelopes isn't it? If people didn't push the envelope we'd all be living in trees picking nits off each other.

Frosty The Lucky.

 

[Another FrankenBurner]

You can also mail stuff. 

[Mikey98118]

Speaking of stuff. I figure you have more good ideas for stuff. We need to encourage you to cough up more of them wild thoughts floatin' 'round in your head

[Frosty]

I've been watching a lot of science channels on youtube. Ever hear of, Isaac Arthur? Ignore the speech impediment I have yet to watch one of his videos that was less than excellent. He's one of those rare guys who can explain some really esoteric science and make it understandable. . . I think anyway. 

Right now I have too many wild ideas in my head to put much together that meets the blacksmithing requirement here. Then again, maybe not. One of the guys in the club sent me a link to a "Rowan Tailor" video about forging a "Roman Fibula." And now I have ANOTHER channel I'm subscribed to. I don't THINK this violates the rules. I'm going to have to watch it half a dozen time before thinking about attempting it.

 https://www.youtube.com/watch?v=JN2U9_lGovg&ab_channel=RowanTaylor

Frosty The Lucky.

[Mikey98118]

 

 

The 2-1/2 gallon "D" forge

Another variant on two-gallon tunnel forges is a two and a half gallon forge, shaped like a  “D” laying on its side; these are made from the top half of a five-gallon propane cylinder, cut lengthwise; this half has an exhaust opening cut into its front, is lined with refractory, and rests on a steel pan, which is filled with various refractory layers. Where and what kind of burner or burners will be mounted varies from builder to builder. A narrow ribbon burner can even be mounted in one side of the base pan, rather than burners in the half cylinder top portion of these forges.

[Mikey98118]

h for anything smoldering in a corner or under a bench.

 

Regulators and fuel hoses

There is a lot to know about hoses, different kinds of valves, and other plumbing choices (black hose versus, copper tubing, versus stainless steel braided gas hose, etc.), but, so long as you think about safety FIRST, and avoid doing something thoughtless, all those choices are only about what I call "add-ons." Meaning they can be rearranged at your leisure, giving lots of time to learn the fine points about plumbing your equipment before making a final decision.

    For instance; should you install an idler circuit? That is best done with metal tubing or pipe--not rubber hose. I personally dislike using copper refrigeration tubing to plumb gas equipment; but there is nothing half as good to employ in an idler circuit. We must beware, not to trip over our “druthers.”

    The first piece of equipment attached to your fuel cylinder should be a variable pressure regulator. You cannot use acetylene regulators for any other fuel gas; they are illegal, unsafe, and impractical to use with LPG fuels. While you can use a typical multi-fuel gas industrial regulator, LPG regulators are less expensive and better suited for use with these fuels in cold weather. I recommend using a 0 to 30 PSI model, with a pressure gauge attached, although a 0-20 PSI regulator will serve just fine, most of the time.

    You can find good quality 0-30 PSI propane regulators offered on eBay, Amazon.com, or  find them locally at large hardware stores. If you end up with a regulator that does not have a pressure gauge, or a side port in which to install one, you can add a “T” pipe fitting at the regulator’s outlet and install a pressure gauge there, using 1/4” short pipe nipples; one for the gauge and one for the gas hose.

 

Caution: NEVER attempt to use water hose, or air hose, to carry fuel gas. Propane can partially dissolve the hose and/or seals on water and air fittings. The first you now of it, may be when the entire hose is suddenly ablaze (I was present when this happened to a friend).

D. O. T cylinders are usually fitted to regular high-pressure black propane appliance hose; this is available with various fitting choices from hardware and appliance stores; I do not recommend it.

Appliance hose is stiff (difficult to work with), overpriced, and seldom comes in twenty-foot lengths.

    Instead, I recommend using regular 1/4” size “T” (multiple fuel grade) twin torch hose in standard lengths. Once you buy the hose, remove the brass guards from both of its ends, and simply pull the red fuel hose away from the green oxygen hose (save that oxygen hose). What you end up with is a highly flexible top-grade fuel hose at a reasonable price, which can be found at any local welding supply store or ordered online. Take care not to end up with oxyacetylene torch hose; it must not be used with LPG fuels.

    Stainless-steel braided fuel hose is steadily decreasing in cost, making them a bargain priced safety item to add between the rest of your fuel hose and the last few feet near heating equipment; or for a few feet between an outdoor fuel cylinder, and a through the wall piping system (or indoor section of hose).

[Mikey98118]

Sodium silicate is a white powder that dissolves in water; it is usually sold in bottles, with the water already added; it is commonly used to glue Perlite together into a solid layer of secondary refractory insulation, as both products melt at about 1900 °F. Sodium silicate is also used to glue refractory fiber products unto other surfaces, like the inside of forge shells (containers). However, when used this way, ceramic blanket should be rigidized completely through all layers, to keep it from de-laminating, and falling away from the glued surface over time.

 

[Mikey98118]

                                                            Hoses

Refillable fuel cylinders are usually fitted to standard high-pressure black propane appliance hose; this is available with various connector fitting choices from hardware and appliance stores; I do not recommend it. Appliance hose is stiff (difficult to work with), seriously overpriced, and seldom comes in twenty-foot lengths.

    Instead, I recommend using 1/4” size “T” (multiple fuel grade) twin torch hose in standard lengths. Once you buy the hose, remove the brass guards from both of its ends, and simply pull the red fuel hose away from the green oxygen hose (save the oxygen hose). What you end up with is a highly flexible top-grade fuel hose at a reasonable price, which can be found at any local welding supply store or ordered online. Take care not to end up with oxyacetylene torch hose; it must not be used with LPG fuels.

Fuel gas regulator outlet bushings: Torch hose fittings (on the red fuel hose), have left hand thread; this is meant to keep people from mounting the wrong hose on equipment. Thus, you require a special connector, called a fuel Gas regulator outlet bushing, to connect left-hand fuel hose connectors to right hand ¼” pipe thread, which is found on most regulators, needle valves, etc. These bushings come in different sizes to mate up with different hose sizes. “B” size bushings match up with ¼” torch hose.

    Stainless-steel braided fuel hose is a bargain priced safety item to add between the rest of your fuel hose and the last few feet near heating equipment; or for a few feet between an outdoor fuel cylinder, and a through the wall piping system (or indoor section of hose); it is sold in various finish lengths, up to twenty feet.

Caution: NEVER attempt to use water hose, or air hose, to carry fuel gas. Propane will partially dissolve the hose and/or seals on water and air fittings. The first you now of it, might be when the entire hose is suddenly ablaze (I was present when this happened to someone; he was able to run outside, and shut off the feed from his propane cylinder before his shack caught fire). Do not use acetylene rated hose for any LPG (liquid petroleum gas) fuel; it is likely to fail just like water or air hose, because LPG will cause it to decompose.

[Mikey98118]

So why are the powers that be determined that you never switch fuel and oxygen hoses? While the oxygen hose might or might not do okay as a fuel hose, that isn't true of the fuel hose, if hooked up to a source of pure oxygen; it would likely go up in flames.

[Mikey98118]

                                                   Clam shell forges, and...

Jay Hayes is probably the originator of the modern oval shaped gas forge; he certainly is the first to begin selling them (about two decades before anyone else). But, I think he had already been experimenting with clam shell forges for some time, before that. It was in trying to research clam shell forges that I came across Jay's website.

  Clam shell forges have limited utility. If you aren't into armor, metal bowls, or  Spanish style wrought iron, chances are poor that they will be of interest to you. Classic wrought iron used to be one of my hobbies, so I added a form of clam shell forge (the top) on a hot-work table. A vertical up-facing burner built into the table completed the forge; it could also be used for a brick pile forge, and to provide  a very hot flame for reheating hot glass.

    For this to work out in the real world, its clam shell top must be conected to an adjustable height, foot operated pop-up scaffold. You will also want to employ a idler-circuit on the burner's plumbing, to make opening up that top much more comfortable.

The point of all this, is to suggest the path to making practical use for way cool, but marginal, equipment. As Frosty has pointed out, universal tooling seldom works as well as dedicated tooling. But tooling that is too dedicated can be so, well..limited.

  So, a little mixing and matching of equipment might just limit both problems

[Mikey98118]

                                                                     Micro forges

The starting point for Micro forges only begins at coffee-can (one gallon) size. Smaller tin cans, and two-brick forges can take the internal dimensions down as far as you want to go. But, the question is, what are they good for?

  The obvious answer is that they are mainly used by jewelers. However, jewelers punches are far from the only small hand tools that are easily made; but then need hardened and tempered. Miniature screw drivers and other driving tools (ex. hex wrenches) are either way over priced, or cheap imports. You probably don't want to make them from scratch, but the abillity to harden and temper those cheap imports can bring some of them up to usable quality.

However, we don't swat flies with cannons. Trying to heat miniature tools in normal sized forges is equally foolish.

[Mikey98118]

The point of gas forges is to conserve heat. Even a second rate propane forge can enable you to heat steel better than the largest rose-bud on an oxyacetylene torch, for a small fraction of the running costs.

However, a properly designed forge can run rings around that second rate tool. If you want to design a first rate forge, you need to know what goes where, and why.

So, lets discuss the WHY of insulation and finish coats inside your forge. Obviously, the layers of insulation are there to slow heat loss through conduction, but why should that be so very important? No, it isn't about some desperate attempt to conserve all the energy possible. If your forge was just a steel pipe, devoid of a scrap of insulation, the bulk of heat loss would still be straight out of the exhaust opening; not that steel wall.

The main point of insulating the forge's interior surfaces is to deliberately build the level of incandescence on those surfaces. As a forge's internal surface temperature rises, so does the percentage of energy transferred to your work pieces by radiant energy. Past 2000 F the majority of energy transferred  by radiant energy is greater than that transferred directly from the gas flame; and that process only becomes stronger as the color scale goes up.

This brings us to finish coatings. Slowing heat loss by conduction is accomplished in two ways; insulation, and heat reflection. We call it heat reflection, rather than radiant reflection, because what is actually going on is re-emission of radiant energy from incandescent surfaces. All the heat that is being emitted and re-emitted from surfaces isn't available to be lost through conduction, making the insulation work harder to do its job.

High alumina refractory will re-emmit around 70 percent of heat, if the surface particals are small enough; the rougher the surface the more that figure gets slashed. Zirconium oxide will re-emmit over 90 percent of heat enery, if the particles that make up it surface are small enough.

So, how small is that? Small enough to remain in in solution with water; colloidal is how small. So, by starting with zirconium flour, and dissolving some in water, the amount that stays in solution will tell you what percentage is colloidal; that should be nearly all of it. Apply the same test to any refractory oxide you are considering; like, for instance Zircopax 

[Mikey98118]

“D” forges: Are usually less portable than tunnel or oval forges; they should be mounted on a table, unless they are constructed with very rigid bottoms. Both tunnel and oval forges do a better job of shedding excessive heat from their shells. There is no denying that the “D” on its side shape is a much easier and cheaper forge to build than an oval; its floor is completely flat, making it natural to employ Thermal Ceramic’s (a Morgan company) K26 tough and highly insulating firebrick as their floors, and ceramic board and/or Perlite under the brick as secondary insulation. The vault (top section of the shell) can be shaped by bending sheet metal over a propane cylinder, or cutting a pail in half. Rigidized ceramic wool will stay in place under the vaulted (arched) portion of its shell. Miniature “D” forges are often built from old mail boxes.

[Mikey98118]

 

                                                 Exhaust size and shape 

One thing backyard casters and blacksmiths both worry over is how large to make the exhaust openings on their equipment. Too small and you have high back pressure killing burner performance; too large and you can't retain enough heat to do your work. Of course, the closer to the "right" opening size your equipment is the stronger the forge or furnace can be built. Just don't confuse the right size for a “perfect” size. As long as burner output can by varied (turn-down range), there can't be any such thing as a perfect opening size. The right size is what is needed to accommodate the burner's highest output (the highest you are willing to take it to).

    Variable is the optimal opening size; all other dimensions can be outright wrong, but are seldom just right, with a burner flame that can be varied. This is one of the many reasons for controlling exhaust flow with an external baffle wall beyond a larger than needed ringed exhaust opening; thus, allowing the least heat loss through radiation, while maintaining optimal atmospheric pressure in the forge. Why include a ring around the exhaust opening? To divert hot exhaust gasses away from the shell, where it can super-heat its metal.

    If you decide on a movable brick baffle wall in front of the forge, keep the bricks at a small distance from the exhaust opening, to allow hot gases to move up and out, between the opening and brick, while bouncing most radiated heat off of a re-emissive (heat reflective) coating on the bricks, and back into your forge. Keep the stock entrance only as large as is needed to move parts through.

    This arrangement helps to slow the flow of expended gas in the forge interior, as it heads toward the exhaust opening; and then speeds the gas up through the opening; another desirable trade off. So, you are gaining hang time for the heated gas in the forge, and recuperative savings from bounce-back of radiant energy; a win-win situation. A baffle wall also minimizes infrared and white light from impacting your eyes and skin, improving your health and comfort.

                                                                Doors

Maximum part clearance can be provided with a hinged and latched forge door (stainless-steel toggle latches are your best choice); it should contain built-in interchangeable baffle plates (high alumina kiln shelves are perfect for this). A door makes building the refractory structures inside of equipment much easier, and permits larger parts to be heated than would pass through a narrowed exhaust opening. Best of all, it allows closely contoured movable internal baffles to be employed, which would not pass through a narrowed exhaust opening; this promotes the use of single burners for small pieces, saving money in tunnel, oval, and “D” forges, which are run by two or more burners; on these forge shapes, the door is a big step up from an exterior brick baffle wall; it should include a parts entrance that can be varied in size; for instance, with several round (or hexagonal) kiln shelves with different openings cut into them (for passing stock through); these can be exchanged, and held within a pocket structure on the door. These improvements don’t all need to be seen to at once, so long as a hinged and latched door is included in the forge shell. Some people prefer a vertical or horizontal sliding door, instead of hinges.

     High alumina kiln shelves are seven times more insulating than hard fire brick; they are very tough at incandescent temperatures, which is an important consideration for something you will end up shoving parts back and forth through. Exchangeable kiln shelves, with different part openings drilled and cut into them is fine, but building an elaborate system of moving kiln shelf parts to ape the ability of bricks to infinitely vary their openings comes under the heading of "gilding the Lilly." The additional energy savings it provides probably is not worth the effort. Make up new openings in door mounted shelves sparingly.

    Diamond coated and carbide coated rotary burrs (and diamond or carbide coated hole saws) are the preferred way to drill holes in kiln shelves. Friction cutoff blades and diamond coated blades are the best ways to cut out straight lines between those holes.

    A hinged and latched door, can also work on a box forge. Yet, movable bricks, trapped in an angle iron frame will work out better than the hinged door. Furthermore, the angle frame works best, by sliding up and down; counter balanced by a weighted wire, and running through pulleys, or simply sliding sideways.

    You want to coat the hot-face side of either kind of door with one of the re-emission coatings. You can use a formula of 95% zirconia silicate powder (crushed zircon) and 5% Veegum (or 5% bentonite as an alternate); this mixture makes a tough heat reflection coating for wear surfaces. The ingredients should be available in ceramic supply stores. Zirconium silicate can also be mixed with fumed silica to make a tuff and heat reflective coating on hard refractories (but not on ceramic fiber products). There are other choices, Like Plistix 900F, but none of them are easily purchased in other countries. Zirconium silicate and bentonite clay should be readily available in pottery supply stores, all over the globe.

Note: fumed silica in water is also known as colloidal silica. Silica (silicon oxide) is the main ingredient in common glass. However, glass has a much lower melting temperature than silica, because lime and potash are mixed into it, for the express purpose of lowering melting temperatures (the lime), and promoting the process of melting (the potash). Fumed silica melts initially, because the powder’s particles are so small that it has a tremendous amount of surface area, to promote the melting process. After the initial firing, this silica becomes glass like, and remelting it would take far higher temperatures. This is why fumed silica easily melts (once) on the surface of ceramic fibers, to make rigidizer on fiber insulation. And why it also works as one of the binders in some high alumina refractories.

                                                        Casting furnace lids

All these advantages can also be applied in casting furnace mode, if a round kiln shelf is placed in a hoop, which can be swung into position above the furnace and swung out of the way during crucible removal. A mall center hole in the shelf allows observation and metal to be added to the melt; it also provides a rest for preheating metal to make sure it is thoroughly dry before placement in the crucible. But the hot exhaust gasses will heat re-emission coatings into incandescence, causing energy to be radiated back into the furnace.

[Mikey98118]

Copper fittings for ¼” copper refrigeration tubing have 6.35mm openings; making them perfect for brazing, or soldering 6mm and 1/4" brass tubes together to make short radius right angle joints, when plumbing fan-induced burners. Buy these fittings online, or down at your local hardware store. Copper fittings are also the obvious choice to join copper refrigerator tubing to brass tubing, both in burner construction, and to plumb between idler circuits and burners on forges.

Note: Hard rubber tubing is at least semi-insulating, which is why it is used over metal refrigerant pipes on industrial equipment. Copper is a conductor, which is my main objection to its use as burner plumbing. I want the incoming cold fuel gas to help cool the burner's mixing tube, as a safety measure. However, that same rubber tubing can be slit, and used to cover copper refrigeration tubing, with a little help from electrical tape.

[Mikey98118]

Most people with the "get up and go" required to seriously consider building their own forge, assume that, given enough thought and luck, it will be perfect; wrong! No matter how well you do, or how good it is, it shall not be perfect (even if it is), because you well think of half a doesn't improvement after its constructed. Thus, even the perfect gas forge becomes unsatisfactory; it is what it is, no matter how much we itch to make it different

So, I suggest that a novice BUY a Mister Volcano forge first, and build their first forge second.

[Frosty]

Exactly and the first forge you build will practice you up to build your second and so on.  It's like another one of Murphy's laws isn't it Mike?

Say Mike, do you have your auto correct turned on? Your post has "Doesn't" where you clearly meant "Dozen." I have to reset MY preferences, especially turn autocorrect off every darned time  my OS updates and resets everything to default.

Frosty The Lucky.

[Mikey98118]

I have a limited auto correct, when writing the next book on my computer. If I cut and paste some of it onto this site, the auto correct even improves. But, when typing from scratch here, there is nothing whatsoever; never was.

[Frosty]

Yeah, I find weird changes made to my posts sometimes too. I tend to do a lot of edits correcting autocorrect type things. It's getting harder and harder to reset my preferences too, it's like the ITs prefer the defaults. 

Frosty The Lucky.

[Mikey98118]

Hey, if you like what's going on, just wait; it can always get worse

[arkie]

I don't have any experience with gas forges, but with coal getting nearly impossible to get in my area and charcoal (which I'm using now) is expensive (no, I'm not gonna make my own...), I'm considering getting a Mr. Volcano to supplement my main solid fuel forge for the small stuff.  Why fire up a forge and burn lots of fuel for a small item...?  Very inefficient.  I can buy a Mr. Volcano for the cost of about 3 bags of lump char.

[Mikey98118]

 I ran across Ron Reil's gas burner pages on the net, while doing research for my first forge. That was back in 1999; he started building gas forges several years before that, do to the same troubles with his coal forge.